Geologic Map of the Maysville Quadrangle, Chaffee County, Colorado

pebble, and cobble gravel in a silty sand matrix. Most clasts are angular to subangular
and weathered, but Mount Princeton quartz monzonite fragments are generally
disintegrated (grussified). Surface boulders are rare, and those exposed are more than
75% buried below surface of moraine. Moraine surface is very smooth and crest is very
broad and gentle. Soils are strongly developed and have an argillic B-horizon. Degree of
clast weathering, soil development, smooth surface morphology, and disconnection from
present valley axes suggest an early Pleistocene age. Maximum thickness is unknown but
may be more than 100 ft in the graben at the range front between the North Fork and Lost
Creek, where unit is buried by younger colluvium (Qco/Qpbt).
Qpbt2 Pre-Bull Lake till, younger (early to middle Pleistocene) – Heterogeneous
deposits of gravel, sand, silt, and clay deposited by ice in ground () moraines. Deposits
lie far from present streams, outside Bull Lake moraines, and generally form smooth
erosional remnants at the head of the range-front piedmont at Squaw Creek, Walden
Gulch, North Fork, Cree Creek, and South Arkansas River. Forms a high pediment
surface west of the North Fork. At the head of Blank Gulch this till grades into the head
of contemporaneous outwash (Qpbo). Deposits are yellowish-gray, poorly sorted,
unstratified or poorly stratified, matrix-supported, boulder, pebble, and cobble gravel in a
silty sand matrix. Most clasts are angular to subangular but very weathered and pitted.
Surface boulders are minor, and those exposed are more than 75% buried below surface
of moraine. Moraine surface is very smooth and crest is very broad and gentle. Soils are
strongly developed and have an argillic B-horizon. Degree of clast weathering, soil
development, smooth surface morphology, and disconnection from present valley axes
suggest an early Pleistocene age. Maximum thickness is unknown but may be as much as
100 ft near the range front, thinning downslope.
Qpbt1 Pre-Bull Lake till, older (early to middle Pleistocene) – Heterogeneous
deposits of gravel, sand, silt, and clay deposited by ice possibly in ground moraines.
Mapped only between the North Fork and Lost Creek. Deposits lie far from present
streams, outside Bull Lake moraines, and generally form very high erosional remnants on
the range-front. Deposits are yellowish-gray, poorly sorted, unstratified or poorly
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